This is a study of the effects that lead has on the health of the central nervous system (for example, memory), peripheral nervous system (for example, sensation and strength in the hands and fingers), kidneys, blood pressure, and the blood forming system. A total of 803 lead workers and 135 persons without occupational lead exposure are being studied in South Korea. Lead in the body is being assessed by measurement of blood lead, chelatable lead (an estimate of lead in the tissues), and lead in bone. Subjects are tested three times each over three years. Several genetic factors are also being assessed for the role they play in the health effects of lead. These genes are known to differ among individuals. We are interested to know whether different forms of the same genes can modify the effect lead has on health.